This disclosure relates to a device that is operationally and functionally suitable for inclusion in a module in a (Controller Area Network) CAN system with CAN connection.
Specifying, verifying and validating CAN systems with the object of obtaining sufficient information to ensure reliable functioning throughout the whole life of a system is already known. In association with this, reference is made to instruments of various kinds that are available on the market for analysing CAN buses, for example CANalyzer from Vector Informatik GmbH, X-analyser from Warwick Technologies Ltd, and CANlab from Accurate Technologies Inc., all of which are PC-based software that, in conjunction with various CAN/PC interfaces from Kvaser AB, for example LAPcan, can retrieve, timestamp and send messages and error frames on the bus in order to determine the appearance in relation to time of messages on the bus and if and when errors appear. In addition, there are other instruments, for example CAN Scope from Vector Informatik that can measure voltage levels on the CAN bus as a function of the time and, using the rules of the CAN protocol, can display an interpreted image in which the voltage levels are displayed as CAN bits. There are also conventional oscilloscopes incorporating corresponding interpretation. Kvaser markets a product, Memorator, by means of which a large number of messages can be time stamped and saved for later analysis.
A well-known problem is that CAN Controllers (CCs) can only be set to certain bit times determined by the frequency of the oscillator that clocks the CC. For example, 1 Mbit/s can not be set at all with a 13 MHz or 33 MHz clock frequency, while with a 12 MHz frequency only the sample points 50% and 66.67% can be selected. For data communication in general, oscillators are required with great precision, often 500 ppm down to 20 ppm. For example, the USB standard demands at least 500 ppm precision and USB components often demand tighter tolerances, for example Philips recommends 50 ppm for its ISP1761 USB host controller. The requirement for precision in the CAN standard ISO 11898 is dependent upon Phase_Seg1, Phase_Seg2, SJW, and the bit time. There is thus a difference between the requirement for oscillator precision in a data communication system such as USB and a control system such as CAN. In the former, the precision is given by the specification, while in the latter, it is dependent upon the system construction in an individual system. In communication between a CAN bus and a computer, the communication takes place via an interface. The communication between the interface and the computer often takes place via a serial data communication that demands a precise oscillator frequency, for example USB with 12 MHz and 50 ppm.
It is common in known instruments that they do not have a validation function, whereby the various respective CAN settings and oscillators of the modules connected to a CAN bus can be controlled. There is also a need for a unit forming a CAN module to be able to be connected to the CAN system and to be used for various target and indication cases and, for example, to be used as the source in the system for interpretation and initiation of various functions in the CAN system. The unit must, for example, be able to be connected as a source of interference in the system in association with testing. The unit must be able to be sold as separate to the CAN module or corresponding individual connectable unit. The unit must also be able to work with components that are constructed and function in a simple way. The unit must be able to work with connections of various types (topologies), preferably bus connections but also with optical connections, star-wired connections and/or network connections.